1. Field of the Invention
The present invention relates particularly to a method of detecting toner in a developing unit for developing a latent image formed on a photosensitive material of an electronic duplicator with the toner.
With progress of an information-oriented society, a variety of printers or copying machines are used widely, wherein a latent image formed on photosensitive material is developed by toner in the printer or duplicator employing the electrophotography system, the developed toner image is transcribed to a recording sheet and this transcribed toner image is fixed for the printing purpose.
This developing unit comprises a toner supplying unit for supplying toner, a stirring unit for obtaining a developer by mixing the toner and magnetic powder material called a carrier and a developing roller for supplying this developer to the photosensitive material to deposit the toner to a latent image.
The toner supplying unit is provided with a toner detector for detecting toner, while the stirring unit is provided with a concentration sensor for detecting toner concentration.
Since the toner is deposited to a latent image on the photosensitive material, the amount of toner at the stirring unit is reduced. When the concentration sensor detects a shortage of toner, the toner supply roller of the toner supplying unit rotates and the toner is supplied to the stirring unit.
Meanwhile, a toner is supplied from the toner cartridge in the toner supplying unit. When the toner in the toner cartridge is consumed completely, the toner detector detects such condition and indicates a need for replacement of the toner cartridge. However, in case the toner is adhered to the detecting surface of the toner detector, the toner detector judges that the toner cartridge is filled with the toner and therefore if the toner is actually in the shortage condition, the toner cartridge is erroneously judged to be filled with the toner.
In view of avoiding such erroneous detection, the detecting surface of the toner detector is usually cleaned by a cleaning means which rotates with rotation of the toner supply roller.
2. Description of the Related Art
FIG. 1 is a diagram for explaining an example of developing unit. The photosensitive drum 1 is rotated in the direction of arrow mark A by a motor M.sub.1 and a latent image, for example, of letters is formed on the surface of photosensitive drum 1 by irradiating the surface of photosensitive drum 1 uniformly charged by a precharger 2 with the modulated laser beam 3. This latent image is developed by the developer supplied by the developing roller 7 of the developing unit 4.
The developing unit 4 is formed by the toner supplying unit, stirring unit and developing roller unit and is housed in the housing case 9.
The toner supplying unit comprises a toner cartridge 19, a toner hopper 18 for temporarily holding toner, a toner supplying roller 13 formed by sponge roller to push out the toner from a hole 12, an agitator 14 for stirring the toner, a toner detector 16 providing the detecting surface 15 to detect the toner and a cleaning means 17 for cleaning the detecting surface 15.
The stirring unit comprises a couple of stirring rollers 10, 11 for stirring the toner and the carrier and a concentration sensor 8 for detecting toner concentration.
The developing roller unit comprises a magnet roller 5 for attracting the carrier and a non-magnetic sleeve 6 for supplying such attracted carrier and toner to the surface of photosensitive drum 1.
As shown by the arrow mark B, the non-magnetic sleeve 6 of the developing roller 7 rotates in the inverse direction to a magnet roller 5 and the toner attracted by the carrier which is also attracted by the non-magnetic sleeve 6 is adhered to a latent image on the photosensitive drum 1 by the field formed by the magnet roller 5 and thereafter developing is carried out.
When a recording sheet 21 carried by a couple of feed rollers 20, 22 and a sheet guide 23 comes into contact with the surface of photosensitive drum 1, a developed toner image is transcribed to the recording sheet 21 charged by a charging unit for transcription (not illustrated).
The stirring rollers 10, 11 are respectively rotated in the directions indicated by the arrow marks C and D by the motor M.sub.2 in order to stir the carrier and toner. Accordingly, the toner is adhered to the surface of carrier. The toner concentration may be measured by a concentration sensor (permeability sensor) 8 to measure the toner concentration utilizing the property that when a larger amount of toner is adhered to the carrier surface, the flux density passing through the carrier particles is as much reduced. When the toner concentration becomes lower than a constant value, a signal is input to a control unit (not illustrated) and the motor M.sub.3 starts to rotate. Thereby, the toner supplying roller 13 and agitator 14 rotate and the toner in the toner hopper 18 is supplied to the stirring unit from a hole 12 provided at the internal wall of the case 9 by means of the sponge roller of toner supplying roller 13.
In this case, a cleaning means 17 provided to the toner supplying roller 13 rotates simultaneously to conduct the cleaning for the toner adhered to the detecting surface 15 of the toner detector 16. The detecting surface 15 projects within the hopper 18 and toner may be detected depending on the fact that toner is adhered to the surface of detecting surface 15 or not.
The toner is replenished to the toner hopper 18 from the toner cartridge 19, but when the toner in the toner cartridge 19 is used up and toner in the supply of toner hopper 18 becomes low, the toner around the detecting surface 15 is removed and after the surface of the detecting surface is cleaned, the toner is no longer adhered. Accordingly, the toner detector 16 sends the signal indicating "no-toner" condition to the controller to indicate replacement of toner cartridge 19 by a display, for example.
FIG. 2 is a diagram for explaining an example of a cleaning means. The detecting surface 15 of toner detector 16 is projected within the toner hopper 18. If the toner is continuously adhered to the surface, the toner is judged to be existing even after the toner in the toner hopper 18 becomes low, and replacement of toner cartridge 19 cannot be indicated. Therefore, in case a cleaning means 17 formed, for example, by the narrow rectangular type silicon rubber is attached to the shaft of toner supplying roller 13, when the toner supplying roller 13 rotates, the end part of the cleaning means 17 wipes the detecting surface 15 for the cleaning purpose.
The toner supplying roller 13 does not rotate continuously so long as the quantity of toner in the stirring unit is not too low and usually it makes only a single or half turn. In case the cleaning means 17 is in contact with the detecting surface 15 of toner detector 16, the toner detector 16 recognizes "existence of toner" and thereby if the toner does not remain in the toner hopper 18, judgement of "existence of toner" will be made erroneously.
In view of avoiding such erroneous determination, it is essential to detect the position where the cleaning means 17 is not in contact with the detecting surface 15 and to collect detected result of toner detector 16 in this case. Therefore, it is required to provide a position detecting means such as a photoencoder to the shaft of toner supplying roller 13 or to the shaft of motor M.sub.3 and the control unit calculates the position where the cleaning means 17 is not in contact with the detecting surface 15 based on the position information detected by such position detecting means. Namely, it is recommended that the toner detection is preferably carried out while the cleaning means 17 is obviously not in the contact with the detecting surface 15.
As a result, a structure of the control unit is complicated and a problem rises here that the developing unit 4 becomes expensive since hardware such as a photoencoder is provided. Therefore, it has long been expected to propose a simplified method which further determine accurately existence of the toner.
Some references of the method in this technical viewpoint have been proposed. The Japanese Laid-open Patent No. 58-130366 [Application Date: Feb. 29, 1982, by S. Suda, Canon Inc.] proposes a structure under the condition that an output of a toner sensor does not change even when the stirring is conducted in the vicinity of the sensor of the toner hopper or when the sensor detecting surface is cleaned. This reference is different from the present invention. Moreover, it is also explained that the cleaning member stops on the sensor detecting surface, but an output of the toner sensor in this case is not explained.
The Japanese Laid-open Patent No. 58-70254 [Application Date: Oct. 23, 1981, by H. Takeda, M. Ishida, Canon Inc.] proposes a method wherein existence of toner is detected simply by duration time of toner sensor output. This reference is different in structure from the present invention which refers to duration time of toner sensor output within the toner supply time by the toner supplying roller. Therefore, when the toner removing member on the detecting surface stops on the sensor detecting surface, existence of toner is recognized without relation to existence of toner.
The Japanese Laid-open Patent No. 57-196274 [Application date: May 28, 1981, by M. Shibusawa, Ricoh] discloses a method where the detecting surface of a toner sensor is cleaned by a movable member once or more for every one cycle of developing (single page printing), cleaning is carried out between development in every page and position control is carried out so that the cleaning member is set to a determined position during the period other than the cleaning period. This reference is different from the present invention in purpose and structure.